1. Field of the Invention
The present invention relates in general to an apparatus for converting outline data representative of an outline of an image such as a letter, a symbol and a graphical representation, into dot data representative of dots to be formed to reproduce the image. More particularly, the present invention is concerned with improvements in such a data converting apparatus.
2. Discussion of the Prior Art
Images such as characters including letters and symbols represented by image data are printed, displayed or otherwise reproduced according to the image data suitably processed by a computer. Commonly, the image data takes the form of dot data indicating whether a dot should be formed in each of picture elements which are the smallest part of picture image and which determine the resolution of the reproduced image. If a batch of dot data representative of all the images available for reproduction is prepared and stored in an image data memory such as a character data memory, the memory should have an extremely large storage capacity. It is therefore desirable to store a batch of outline data representative of the outlines of the images such as the characters, and convert the outline data into the corresponding dot data by suitable data converting means, when the images are printed, displayed or otherwise reproduced by reproducing means, as disclosed in Japanese Patent Publication No. 53-41017.
In order to convert the outline data into the dot data, the outline data is subjected to a filling-in process, in which the outline data is first defined in a two-dimensional coordinate system. More specifically, the outline of the character represented by the outline data is superimposed on a two-dimensional coordinated pixel screen in which picture elements are defined by a plurality of parallel scanning lines parallel to one of X and Y axes. The size of the picture element and the manner in which the picture elements are distributed on the pixel screen correspond to scanning characteristics of reproducing means such as the printer or display. The picture elements correspond to the resolution of the reproducing means. The filling-in process then searches or determines a picture element that lies in the pixel screen within the area defined by the outline of the character and that should be filled with an image dot. This filling-in process is attained by arithmetic calculation such that an image dot may be produced on each picture element where the relationship between the corresponding picture element and the outline satisfies a predetermined requirement. Thus, the area surrounded by the outline is filled with image dots. Then, dot data are produced such that logical values in bits of the dot data may indicate the presence of image dots at the picture elements within the outline of the character.
The predetermined requirement employed in the arithmetic calculation of the filling-in process, however, causes positions of the picture elements lying within the outline of a character to vary, depending upon the position at which the character outline is positioned relative to the coordinated pixel screen, i.e., depending upon the position at which the character is desired to be printed, displayed or otherwise reproduced. In this case, shape of the character as reproduced according to the dot data may differ from the nominal shape represented by the outline data. Especially when the character has a linear or straight outline segment inclined with respect to the X or Y axis in the pixel screen, positions of the picture elements which lie along and within the straight outline segment vary, at different local portions of the straight outline segment. Accordingly, when character is reproduced by the dot data, the portion of the character corresponding to the inclined straight outline segment tends to differ from the intended or desired inclined straight line.